1. Field of the Invention
The present invention relates to an electronic vacuum sensor. More specifically, the invention relates to a disposable electronic vacuum sensor capable of detecting low vacuum pressure for use in medical applications, such as administration of epidural anesthesia.
2. Related Art
A number of medical procedures involve catheterization of patients, such as administration of anesthesia either before or during a medical procedure. Often, the anesthesia must be administered either continuously or at regular intervals to maintain the effects of the anesthesia during an extended medical procedure.
For administration of epidural anesthesia, it is necessary to accurately locate a patient's epidural space by inserting a needle having a special rounded, oval point, such as an epidural needle (also referred to as a Tuohy or a Hostead point needle) between two of the patient's vertebrae, through ligamentum flavum (the tough ligament holding the spine together), and into the epidural space. Once the epidural space is located, a catheter can be inserted through a needle into the epidural space for anesthesia administration. Two methods are currently used to locate the epidural spacer the "hanging drop" method and the "loss of resistance" method.
According to the hanging drop method, a small amount of sterile local anesthesia solution is placed in a needle hub. The solution clings to the hub as the needle is advanced into the patient's spine. When the point of the needle enters the epidural space, the drop of anesthesia is sucked into the needle by a vacuum existing or forming in the epidural space. Thus, the person administering the anesthesia, such as an anesthesiologist, stops moving the needle forward when the drop disappears into the needle.
Under the loss of resistance method, a glass 5 or 10 ml syringe containing either air or a sterile solution is attached to a needle. The anesthesiologist pushes the plunger of the syringe while the needle is being inserted into the patient to determine whether there is any resistance ("bounce"). When there is resistance, the syringe will hold the air or solution, indicating that the point of the needle is still in the ligamentum flavum. When there is no longer any resistance and the anesthesiologist is able to move the plunger forward, the needle is in the epidural space. Thus, the anesthesiologist advances the needle and syringe into the patient's spine until there is a loss of resistance, indicating that the point of the needle has entered the epidural space and the contents of the syringe have emptied into the epidural space.
To insert the needle into the epidural space according to these methods, a great amount of pressure must be applied to the needle to penetrate the tough ligamentum flavum. When applying such pressure, the anesthesiologist may lose feeling of the penetration rate and push the needle beyond the epidural space before detecting either movement of the drop of anesthesia into the needle or a loss of resistance, thereby puncturing a hole in the arachnoid membrane and causing leakage of central spinal fluid (CSF) from the spinal fluid space. Loss of CSF may cause the patient to have severe headaches (often called "spinal headache"). Also, puncture of the arachnoid membrane may result in infection of the spinal cord or meningitis.
Therefore, it is desirable to provide a sensitive device and method for detecting a relatively small vacuum pressure, so that the epidural space can be safely and easily located. It is also desirable to provide a disposable, inexpensive vacuum sensor shaped so that it is easily handled and gripped during use.